1. Field of the Invention
The present invention relates in general to electrochromic devices and, more particularly, to a tristate electrochromic device having anodic and/or cathodic materials which, upon application of different applied potentials, can selectively absorb predetermined wavelengths of electromagnetic radiation, including visible radiation (i.e. visible light ranging in wavelength from approximately 400 nanometers (nm) to approximately 750 nm) and/or near-infrared radiation (i.e. heat ranging in wavelength from approximately 750 nm to approximately 2,400 nm) and vice versa—depending upon the device configuration.
2. Background Art
Electrochromic devices have been known in the art for several years. Furthermore, the utilization of a plurality of anodic and/or cathodic materials in the medium of an electrochromic device is well known. See, for example, U.S. Pat. No. 5,998,617 entitled “Electrochromic Compounds,” U.S. Pat. No. 6,020,987 entitled “Electrochromic Medium Capable Of Producing A Pre-selected Color,” U.S. Pat. No. 6,037,471 entitled “Electrochromic Compounds,” U.S. Pat. No. 6,141,137 entitled “Electrochromic Media For Producing A Pre-selected Color,” U.S. Pat. No. 6,193,912 entitled “Near Infrared-Absorbing Electrochromic Compounds And Devices Comprising Same,” and U.S. application Ser. No. 10/283,506 entitled “Electrochromic Device Having An Electron Shuttle,” all of which are hereby incorporated herein by reference in their entirety.
While the above-identified references disclose utilizing a plurality of anodic and/or cathodic materials in the medium of an electrochromic device, to the best of Applicant's knowledge, they do not enable a user to selectively absorb light in the visible or near-infrared region simply by varying the applied potential. The inability to operate in this manner has caused prior art devices to be limited in a number of applications.
For example, during hot summer days when the sun is well above the horizon, it may be desirable for an electrochromic device to substantially absorb near-infrared radiation (i.e. heat) without substantially absorbing visible radiation so that an environment (i.e. room, building, etcetera) remains both temperate as well as sufficiently illuminated. However, as the sun approaches the horizon during, for example, periods generally after sunrise and/or before sunset, it may be desirable for an electrochromic device to substantially absorb both near-infrared radiation (i.e. heat) as well as visible radiation (i.e. light), to, in turn, reduce glare and/or undesirable illumination effects associated with the same.
During winter days in cold climates it may be desirable to have a device absorb only visible light during the coldest morning hours when the sun is low on the horizon and to allow the near-infrared light to enter and allow some solar warming of the interior of the building, while at the same time reducing unwanted glare. When the sun is higher in the sky, the device could be turned off to allow both visible light and near-infrared radiation to enter the building, thereby reducing the need for artificial illumination and allowing for solar heat to enter the building. Later in the afternoon, it may be desirable to block both the visible and near-infrared radiation for thermal and visual comfort.
It has now been surprisingly discovered that selective utilization of one or more anodic and/or cathodic electroactive materials enables an electrochromic medium, and, in turn, an electrochromic device, to operate between at least three regions or states (referred to as a tristate device), namely (1) a first state (i.e. when a potential difference less than that sufficient to cause electrochemical oxidation or reduction of the anodic and cathodic materials is applied, a.k.a. the open circuit state or high transmission state) wherein the device has its maximum light transmission; (2) a second state (i.e. an applied potential between the minimum potential where oxidation or reduction of the anodic and cathodic materials occurs up to a “second” potential difference) wherein variable attenuation of either visible radiation or near-infrared radiation occurs to a significant extent depending on the device configuration without significant attenuation in the other spectral region; and (3) a third state (i.e. an applied potential between the “second” potential and a “third” potential difference) wherein variable attenuation occurs to a significant extent in the other spectral region depending on device configuration. It will be understood that attenuation refers to the relative change in transmission of a device as the potential is changed.
It is therefore an object of the present invention to provide a tristate electrochromic device that remedies the aforementioned limitations associated with conventional electrochromic devices.